Fix cascading deletion gaps for user and team cleanup

- Add ON DELETE CASCADE to users_teams, oauth_providers, admin_permissions
  and ON DELETE SET NULL (with nullable columns) to team_api_keys.created_by,
  hosts.created_by, host_tokens.created_by so HardDeleteExpiredUsers no longer
  fails with FK violations
- User account deletion now cascades to sole-owned teams via DeleteTeamInternal,
  preventing orphaned teams with live sandboxes after account removal
- ListActiveSandboxesByTeam now includes hibernated sandboxes so their disk
  snapshots are cleaned up during team deletion
- Team soft-delete now hard-deletes sandbox metric points, metric snapshots,
  API keys, and channels to prevent data accumulation on deleted teams
- Extract deleteTeamCore() to deduplicate shared logic across DeleteTeam,
  AdminDeleteTeam, and DeleteTeamInternal
- Fix ListAPIKeysByTeamWithCreator to use LEFT JOIN after created_by became
  nullable, and update handler to read pgtype.Text.String for creator_email

db/migrations/20260415221116_cascade_user_delete.sql

@@ -0,0 +1,72 @@
+-- +goose Up
+
+-- users_teams: remove membership when user is deleted
+ALTER TABLE users_teams DROP CONSTRAINT users_teams_user_id_fkey;
+ALTER TABLE users_teams ADD CONSTRAINT users_teams_user_id_fkey
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+
+-- oauth_providers: remove auth links when user is deleted
+ALTER TABLE oauth_providers DROP CONSTRAINT oauth_providers_user_id_fkey;
+ALTER TABLE oauth_providers ADD CONSTRAINT oauth_providers_user_id_fkey
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+
+-- admin_permissions: remove permissions when user is deleted
+ALTER TABLE admin_permissions DROP CONSTRAINT admin_permissions_user_id_fkey;
+ALTER TABLE admin_permissions ADD CONSTRAINT admin_permissions_user_id_fkey
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+
+-- team_api_keys.created_by: make nullable, SET NULL on user delete
+ALTER TABLE team_api_keys ALTER COLUMN created_by DROP NOT NULL;
+ALTER TABLE team_api_keys DROP CONSTRAINT team_api_keys_created_by_fkey;
+ALTER TABLE team_api_keys ADD CONSTRAINT team_api_keys_created_by_fkey
+    FOREIGN KEY (created_by) REFERENCES users(id) ON DELETE SET NULL;
+
+-- hosts.created_by: make nullable, SET NULL on user delete
+ALTER TABLE hosts ALTER COLUMN created_by DROP NOT NULL;
+ALTER TABLE hosts DROP CONSTRAINT hosts_created_by_fkey;
+ALTER TABLE hosts ADD CONSTRAINT hosts_created_by_fkey
+    FOREIGN KEY (created_by) REFERENCES users(id) ON DELETE SET NULL;
+
+-- host_tokens.created_by: make nullable, SET NULL on user delete
+ALTER TABLE host_tokens ALTER COLUMN created_by DROP NOT NULL;
+ALTER TABLE host_tokens DROP CONSTRAINT host_tokens_created_by_fkey;
+ALTER TABLE host_tokens ADD CONSTRAINT host_tokens_created_by_fkey
+    FOREIGN KEY (created_by) REFERENCES users(id) ON DELETE SET NULL;
+
+-- +goose Down
+
+-- Revert host_tokens.created_by
+ALTER TABLE host_tokens DROP CONSTRAINT host_tokens_created_by_fkey;
+UPDATE host_tokens SET created_by = '00000000-0000-0000-0000-000000000000' WHERE created_by IS NULL;
+ALTER TABLE host_tokens ALTER COLUMN created_by SET NOT NULL;
+ALTER TABLE host_tokens ADD CONSTRAINT host_tokens_created_by_fkey
+    FOREIGN KEY (created_by) REFERENCES users(id);
+
+-- Revert hosts.created_by
+ALTER TABLE hosts DROP CONSTRAINT hosts_created_by_fkey;
+UPDATE hosts SET created_by = '00000000-0000-0000-0000-000000000000' WHERE created_by IS NULL;
+ALTER TABLE hosts ALTER COLUMN created_by SET NOT NULL;
+ALTER TABLE hosts ADD CONSTRAINT hosts_created_by_fkey
+    FOREIGN KEY (created_by) REFERENCES users(id);
+
+-- Revert team_api_keys.created_by
+ALTER TABLE team_api_keys DROP CONSTRAINT team_api_keys_created_by_fkey;
+UPDATE team_api_keys SET created_by = '00000000-0000-0000-0000-000000000000' WHERE created_by IS NULL;
+ALTER TABLE team_api_keys ALTER COLUMN created_by SET NOT NULL;
+ALTER TABLE team_api_keys ADD CONSTRAINT team_api_keys_created_by_fkey
+    FOREIGN KEY (created_by) REFERENCES users(id);
+
+-- Revert admin_permissions
+ALTER TABLE admin_permissions DROP CONSTRAINT admin_permissions_user_id_fkey;
+ALTER TABLE admin_permissions ADD CONSTRAINT admin_permissions_user_id_fkey
+    FOREIGN KEY (user_id) REFERENCES users(id);
+
+-- Revert oauth_providers
+ALTER TABLE oauth_providers DROP CONSTRAINT oauth_providers_user_id_fkey;
+ALTER TABLE oauth_providers ADD CONSTRAINT oauth_providers_user_id_fkey
+    FOREIGN KEY (user_id) REFERENCES users(id);
+
+-- Revert users_teams
+ALTER TABLE users_teams DROP CONSTRAINT users_teams_user_id_fkey;
+ALTER TABLE users_teams ADD CONSTRAINT users_teams_user_id_fkey
+    FOREIGN KEY (user_id) REFERENCES users(id);